Learning: Mechanisms, Ecology, and Evolution • 21lution of sociality in ants, wasps, and bees. Extensive learning is also required
in all species consuming prey that is challenging to capture or handle. This
category includes many species of birds and mammals and numerous other
taxa. Examples include fish-eating birds (e.g., Daunt et al. 2007), oystercatch-
ers (Norton-Griffiths 1969), and cheetahs (Caro 1994). In sum, learning is a
precondition allowing the occupation of many niches, and it determines key
ecological interactions such as competition and predation.
2.6.2. l i f e h ist ory of l e a r n i ng
Life history research has focused on the effects of three physical factors—
growth, effort, and senescence—on reproductive success (Stearns 1992; Roff
2002). The effects of learning have been noted, especially in a few long-term
avian studies (Nol and Smith 1987; Wooler et al. 1990; Black and Owen
1995; Rattiste 2004), but the relative contribution of learning to performance
throughout the life span has not been examined closely. In animals that reach
final growth before sexual maturity, the three major contributors to reproduc-
tive success are effort, physiology, and learning. Reproductive effort is defined
as investment in current reproduction that decreases future reproduction or
survival. Although it is commonly asserted that effort should increase with age,
theoretical analyses emphasize that effort could also decrease or plateau with
age (Fagen 1972; Charlesworth and Leon 1976; Taylor 1991; Roff 2002). The
empirical data are mixed, with some studies suggesting increased effort with
age (Pugesek 1981; Clutton-Brock 1984; Candolin 1998; Poizat et al. 1999) and
others documenting no change with age (W. Reid 1988).
Major physiological attributes such as muscle power and endurance increase
early in the life of some species. From sexual maturity onward, physiology
is subjected to senescence, defined as a decrease in body condition, associ-
ated with decreased fertility and survival rates, with increased age (Rose 1991;
Kirkwood and Austad 2000). As with reproductive effort, however, theory and
data indicate that patterns of senescence can diverge from the classical pattern
of exponential increase in mortality rates with age (Abrams 1993; Reznick et
al. 2004; Williams et al. 2006). Overall, we know relatively little about lifetime
patterns of physiological performance in nonhuman animals in the wild.
Learning is somewhat similar to physical growth. Hence, the investment in
learning may be highest before animals reach sexual maturity. Unlike physical
growth, however, some tasks can be learned only by performing them, a fea-
ture referred to as “learning by doing” in the economic literature (Arrow 1962).
Consequently, learning may contribute to a gradual increase in performance
throughout an individual’s life as long as it is not impaired by senescence
(Dukas 2008d).